Control system for an N-methyl-2-pyrrolidone refining unit receiving medium sour charge oil

ABSTRACT

A solvent refining unit treats medium sour charge oil with an N-methyl-2-pyrrolidone solvent, hereafter referred to as MP, in an extractor to yield raffinate and extract mix. The MP is recovered from the and from the extract mix and returned to the refining extractor. A system controlling the refining unit includes a gravity analyzer, a sulfur analyzer, a refractometer and viscosity analyzers; all analyzing the medium sour charge oil and providing corresponding signals, sensors sense the flow rates of the charge oil and the MP flowing into the extractor and the temperature of the extract mix and provide corresponding signals. One of the flow rates of the medium sour charge oil and the MP flow rates is controlled in accordance with the signals from all the analyzers, the refractometer and all the sensors, while the other flow rate of the medium sour charge oil and the MP flow rates is constant.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to control systems and methods in generaland, more particularly, to control systems and methods for oil refiningunits.

2. Summary of the Invention

A solvent refining unit treats medium sour charge oil with anN-methyl-2-pyrrolidone solvent, hereafter referred to as MP, in anextractor to yield raffinate and extract mix. The MP is recovered fromthe raffinate and from the extract mix and returned to the extractor. Asystem controlling the refining unit includes a gravity analyzer, asulfur analyzer, a refractometer and viscosity analyzers. The analyzersanalyze the medium sour charge oil and provide corresponding signals.Sensors sense the flow rates of the charge oil and the MP flowing intothe extractor and the temperature of the extract mix and providecorresponding signals. The flow rate of the medium sour charge oil orthe MP is controlled in accordance with the signals provided by all thesensors, the refractometer and the analyzers while the other flow rateof the medium sour charge oil and the MP flow rates is constant.

The objects and advantages of the invention will appear more fullyhereinafter from a consideration of the detailed description whichfollows, taken together with the accompanying drawings wherein oneembodiment of the invention is illustrated by way of example. It is tobe expressly understood, however, that the drawings are for illustrationpurposes only and are not to be construed as defining the limits of theinvention.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a solvent refining unit in partial schematic form and acontrol system, constructed in accordance with the present invention, insimple block diagram form.

FIG. 2 is a detailed block diagram of the control means shown in FIG. 1.

FIGS. 3 through 13 are detailed block diagrams of the H computer, the Ksignal means, the H signal means, the KV computer, the VI signal means,the SUS computer, the SUS₂₁₀ computer, the VI_(DWC).sbsb.O computer, theVI_(DWC).sbsb.P computer, the ΔRI computer and the J computer,respectively, shown in FIG. 2.

DESCRIPTION OF THE INVENTION

An extractor 1 in a solvent refining unit is receiving medium sourcharge oil by way of a line 4 and N-methyl-2-pyrrolidone solvent,hereafter referred to as MP, by way of a line 7 and providing raffinateto recovery by way of a line 10, which is further processed to yieldrefined oil, and an extract mix to recovery by way of a line 14.

Medium sour charge oil is a charge oil having a sulfur content greaterthan a predetermined sulfur content and having a kinematic viscosity,corrected to a predetermined temperature, less than a firstpredetermined kinematic viscosity but equal to or less than a secondpredetermined kinematic viscosity. Preferably, the predetermined sulfurcontent is 1.0%, the predetermined temperature is 210° F., and the firstand second predetermined kinematic viscosities are 7.0 and 15.0,respectively. The temperature in extractor 1 is controlled by coolingwater passing through a line 16. A gravity analyzer 20, viscosityanalyzers 23 and 24, a refractometer 26 and a sulfur analyzer 28 samplethe charge oil in line 4 and provide signals API, KV₂₁₀, KV₁₅₀, RI andS, respectively, corresponding to the API gravity, the kinematicviscosities at 210° F. and 150° F., the refractive index and sulfurcontent, respectively.

A flow transmitter 30 in line 4 provides a signal CHG corresponding tothe flow rate of the charge oil in line 4. Another flow transmitter 33in line 7 provides a signal SOLV corresponding to the MP flow rate. Atemperature sensor 38, sensing the temperature of the extract mixleaving extractor 1, provides a signal T corresponding to the sensedtemperature. All signals hereinbefore mentioned are provided to controlmeans 40.

Control means 40 provides signal C to a flow recorder controller 43.Recorder controller 43 receives signals CHG and C and provides a signalto a valve 48 to control the flow rate of the charge oil in line 4 inaccordance with signals CHG and C so that the charge oil assumes adesired flow rate. Signal T is also provided to temperature controller50. Temperature controller 50 provides a signal to a valve 51 to controlthe amount of cooling water entering extractor 1 and hence thetemperature of the extract-mix in accordance with its set point positionand signal T.

The following equations are used in practicing the present invention formedium sour charge oil:

    H.sub.210 =lnln (KV.sub.210 +C.sub.1)                      (1)

where H₂₁₀ is a viscosity H value for 210° F., KV₂₁₀ is the kineticviscosity of the charge oil at 210° F. and C₁ is a constant having apreferred value of 0.7.

    H.sub.150 =lnln (KV.sub.150 +C.sub.1)                      (2)

where H₁₅₀ is a viscosity H value for 150° F., and KV₁₅₀ is thekinematic viscosity of the charge oil at 150° F.

    k.sub.150 =[c.sub.2 -ln (T.sub.150 +C.sub.3 ]/C.sub.4      (3)

where K₁₅₀ is a constant needed for estimation of the kinematicviscosity at 100° F., T₁₅₀ is 150, and C₂ through C₄ are constantshaving preferred values of 6.5073, 460 and 0.17937, respectively.

    H.sub.100=H.sub.210 +(H.sub.150 -H.sub.210)/K.sub.150      (4)

where H₁₀₀ is a viscosity H value for 100° F.

    kv.sub.100 =exp[exp(H.sub.100)]-C.sub.1                    (5)

where KV₁₀₀ is the kinematic viscosity of the charge oil at 100° F.

    sus=c.sub.5 (kv.sub.210)+[c.sub.6 +c.sub.7 (kv.sub.210)]/[c.sub.8 +c.sub.9 (kv.sub.210)+c.sub.10 (kv.sub.210).sup.2 +c.sub.11 (kv.sub.210).sup.3 ](c.sub.12)                                               (6)

where SUS is the viscosity in Saybolt Universal Seconds and C₅ throughC₁₂ are constants having preferred values of 4.6324,1.0, 0.03264,3930.2, 262.7, 23.97, 1.646 and 10³¹ 5, respectively.

    SUS.sub.210 =[C.sub.13 +C.sub.14 (C.sub.15 -C.sub.16)]SUS  (7)

where SUS₂₁₀ is the viscosity in Saybolt Universal Seconds at 210° F.and C₁₃ through C₁₆ are constants having preferred values of 1.0,0.000061, 210 and 100, respectively.

    VI.sub.DWC.sbsb.O =C.sub.17 -C.sub.18 (VI)+C.sub.19 (S).sup.2 -C.sub.20 (RI)(API)+C.sub.21 (API)(VI)-C.sub.22 (API)(S)            (8)

where VI_(DWC).sbsb.O is the viscosity of the dewaxed medium sour chargeoil having a pour point of 0° F. and C₁₇ through C₂₂ are constantshaving preferred values of 838.96, 11.504, 3.1748, 19.19, 0.42412 and0.38322, respectively.

    VI.sub.DWC.sbsb.P =VI.sub.DWC.sbsb.O +(Pour)[C.sub.23 -C.sub.24 ln SUS.sub.210 +C.sub.25 (ln SUS.sub.210).sup.2 ]            (9)

where VI_(DWC).sbsb.P and Pour are the viscosity index of the dewaxedproduct at a predetermined pour point temperature and the pour point ofthe dewaxed product, respectively, and C₂₃ through C₂₅ are constantshaving preferred values of 2.856, 1.18 and 0.126, respectively.

    ΔVI=VI.sub.RO -V.sub.DWC.sbsb.O =VI.sub.RP -VI.sub.DWC.sbsb.P, (10)

where VI_(RO) and VI_(RP) are the VI of the refined oil at 0° F., pourand the predetermined temperature, respectively.

    ΔRI=[C.sub.26 -C.sub.27 (ΔVI)-C.sub.28 (KV.sub.210).sup.2 +C.sub.29 (VI).sup.2 -C.sub.30 (KV.sub.210)(API)+C.sub.31 (ΔVI)(KV.sub.210)+C.sub.32 (API)(S)-C.sub.33 (VI)(S)-C.sub.34 (ΔVI).sup.2 ]C.sub.35                               (11)

where ΔRI is the change in the refractive index from the charge oil tothe raffinate, VI is the viscosity index of the medium sour charge oiland C₂₆ through C₃₅ are constants having preferred values of 386.48,14.544, 1.4528, 0.01232, 1.4923, 2.4913, 27.217, 8.3297, 0.056978 and10³¹ 4, respectively.

    J=C.sub.36 +C.sub.37 (ΔRI)+C.sub.38 (S).sup.2 -C.sub.39 (VI).sup.2 +C.sub.40 (T).sup.2 +C.sub.41 (S)(T)-C.sub.42 (KV.sub.210)(T)-C.sub.43 (S)-C.sub.44 (ΔRI)(T)+C.sub.45 (ΔRI)(ΔVI), (12)

where J is the MP dosage and C₃₆ through C₄₅ are constants havingpreferred values of 690.21, 51327, 115.13, 0.078784, 0.034373, 3.7926,0.41528, 974.48, 404.34 and 218.61.

    C=(SOLV)(100)/J,                                           (13)

where C is the new charge oil flow rate.

Referring now to FIG. 2, signal KV₂₁₀ is provided to an H computer 50 incontrol means 40, while signal KV₁₅₀ is applied to an H computer 50A. Itshould be noted that elements having a number and a letter suffix aresimilar in construction and operation as to those elements having thesame numeric designation without a suffix. All elements in FIG. 2,except elements whose operation is obvious, will be disclosed in detailhereinafter. Computers 50 and 50A provide signals E₁ and E₂corresponding to H₂₁₀ and H₁₅₀, respectively, in equations 1 and 2,respectively, to H signal means 53. K signal means 55 provides a signalE₃ corresponding to the term K₁₅₀ in equation 3 to H signal means 53. Hsignal means 53 provides a signal E₄ corresponding to the term H₁₀₀ inequation 4 to a KV computer 60 which provides a signal E₅ correspondingto the term KV₁₀₀ in accordance with signal E₄ and equation 5 ashereinafter explained.

Signals E₅ and KV₂₁₀ are applied to VI signal means 63 which provides asignal E₆ corresponding to the viscosity index.

An SUS computer 65 receives signal KV₂₁₀ and provides a signal E₇corresponding to the term SUS in accordance with the received signalsand equation 6 as hereinafter explained.

An SUS 210 computer 68 receives signal E₇ and applies signal E₈corresponding to the term SUS₂₁₀ in accordance with the received signaland equation 7 as hereinafter explained.

A VI_(DWC).sbsb.O computer 70 receives signal RI, S, API, and E₆ andprovides a signal E₁₀ corresponding to the term VI_(DWC).sbsb.O inaccordance with the received signals and equation 8. Subtracting means76 performs the function of equation 10 by subtracting signal E₁₁ from adirect current voltage V₉, corresponding to the term VI_(RP), to providea signal E₁₂ corresponding to the term ΔVI in equation 10.

A ΔRI computer 79 receives signals E₆, E₁₂, KV₂₁₀, S and API andprovides a signal ΔRI, corresponding to the term ΔRI in equation 11, inaccordance with received signals and equation 11 as hereinafterexplained.

A J computer 80 receives signals T, KV₂₁₀, S, ΔRI, E₆ and E₁₂ andprovides a signal E₁₃ corresponding to the term J in accordance with thereceived signals and equation 12 as hereinafter explained to a divider83.

Signal SOLV is provided to a multiplier 82 where it is multiplied by adirect current voltage V₂ corresponding to a value of 100 to provide asignal corresponding to the term (SOLV)(100) in equation 13. The productsignal is applied to divider 83 where it is divided by signal E₁₃ toprovide signal C corresponding to the desired new charge oil flow rate.

It would be obvious to one skilled in the art that if the charge oilflow rate was maintained constant and the MP flow rate varied, equation13 would be rewritten as

    SO=(J)(CHG)/100                                            (14)

where SO is the new MP flow rate. Control means 40 would be modifiedaccordingly.

Referring now to FIG. 3, H computer 50 includes summing means 112receiving signal KV₂₁₀ and summing it with a direct current voltage C₁to provide a signal corresponding to the term [KV₂₁₀ +C₁ ] shown inequation 1. The signal from summing means 112 is applied to a naturallogarithm function generator 113 which provides a signal correspondingto the natural log of the sum signal which is then applied to anothernatural log function generator 113A which in turn provides signal E₁.

Referring now to FIG. 4, K signal means 55 includes summing means 114summing direct current voltage T₁₅₀ and C₃ to provide a signalcorresponding to the term [T₁₅₀ +C₃ ] which is provided to a natural logfunction generator 113B which in turn provides a signal corresponding tothe natural log of the sum signal from summing means 114. Subtractingmeans 115 subtracts the signal provided by function generator 113B froma direct current voltage C₂ to provide a signal corresponding to thenumerator of equation 3. A divider 116 divides the signal fromsubtracting means 115 with a direct current voltage C₄ to provide signalE₃.

Referring now to FIG. 5, H signal means 53 includes subtracting means117 which subtracts signal E₁ from signal E₂ to provide a signalcorresponding to the term H₁₅₀ -H₂₁₀, in equation 4, to a divider 118.Divider 118 divides the signal from subtracting means 117 by signal E₃.Divider 118 provides a signal which is summed with signal E₁ by summingmeans 119 to provide signal E₄ corresponding to H₁₀₀.

Referring now to FIG. 6, a direct current voltage V₃ is applied to alogarithmic amplifier 120 in KV computer 60. Direct current voltage V₃corresponds to the mathematical constant e. The output from amplifier120 is applied to a multiplier 122 where it is multiplied with signalE₄. The product signal from multiplier 122 is applied to an antilogcircuit 125 which provides a signal corresponding to the term exp (H₁₀₀)in equation 5. The signal from circuit 125 is multiplied with the outputfrom logarithmic amplifier 120 by a multiplier 127 which provides asignal to antilog circuit 125A. Circuit 125A is provided to subtractingmeans 128 which subtracts a direct current voltage C₁ from the signalfrom circuit 125A to provide signal E₅.

Referring now to FIG. 7, VI signal means 63 is essentially memory meanswhich is addressed by signals E₅, corresponding to KV₁₀₀, and signalKV₂₁₀. In this regard, a comparator 130 and comparator 130A represent aplurality of comparators which receive signal E₅ and compare signal E₅to reference voltages, represented by voltages R₁ and R₂, so as todecode signal E₅. Similarly, comparators 130B and 130C represent aplurality of comparators receiving signal KV₂₁₀ which compare signalKV₂₁₀ with reference voltages RA and RB so as to decode signal KV₂₁₀.The outputs from comparators 130 and 130B are applied to an AND gate 133whose output controls a switch 135. Thus, should comparators 130 and130B provide a high output, AND gate 133 is enabled and causes switch135 to be rendered conductive to pass a direct current voltage V_(A)corresponding to a predetermined value, as signal E₆ which correspondsto VI. Similarly, the outputs of comparators 130 and 130C control an ANDgate 133A which in turn controls a switch 135A to pass or to block adirect current voltage V_(B). Similarly, another AND gate 133B iscontrolled by the outputs from comparators 130A and 130B to control aswitch 135B so as to pass or block a direct current voltage V_(C).Again, an AND gate 133C is controlled by the outputs from comparators130A and 130C to control a switch 135C to pass or to block a directcurrent voltage V_(D). The outputs of switches 135 through 135C are tiedtogether so as to provide a common output.

Referring now to FIG. 8, the SUS computer 65 includes multipliers 136,137 and 138 multiplying signal KV₂₁₀ with direct current voltages C₉, C₇and C₅, respectively, to provide signals corresponding to the terms C₉(KV₂₁₀), C₇ (KV₂₁₀) and C₅ (KV₂₁₀), respectively, in equation 6. Amultiplier 139 effectively squares signal KV₂₁₀ to provide a signal tomultipliers 140, 141. Multiplier 140 multiplies the signal frommultiplier 139 with a direct current voltage C₁₀ to provide a signalcorresponding to the term C₁₀ (KV₂₁₀)² in equation 6. Multiplier 141multiplies the signal from multiplier 139 with signal KV₂₁₀ to provide asignal corresponding to (KV₂₁₀)³. A multiplier 142 multiplies the signalfrom multiplier 141 with a direct current voltage C₁₁ to provice asignal corresponding to the term C₁₁ (KV₂₁₀)³ in equation 6. Summingmeans 143 sums the signals from multipliers 136, 140 and 142 with adirect current voltage C₈ to provide a signal to a multiplier 144 whereit is multiplied with a direct current voltage C₁₂. The signal frommultiplier 137 is summed with a direct current voltage C₆ by summingmeans 145 to provide a signal corresponding to the term [C₆ +C₇ (KV₂₁₀]. A divider 146 divides the signal provided by summing means 145 withthe signal provided by multiplier 144 to provide a signal which issummed with the signal from multiplier 138 by summing means 147 toprovide signal E₇.

Referring now to FIG. 9, SUS₂₁₀ computer 68 includes subtracting means148 which subtracts a direct current voltage C₁₆ from another directcurrent voltage C₁₅ to provide a signal corresponding to the term (C₁₅-C₁₆) in equation 7. The signal from subtracting means 148 is multipliedwith a direct current voltage C₁₄ by a multiplier 149 to provide aproduct signal which is summed with another direct current voltage C₁₃by summing means 150. Summing means 150 provides a signal correspondingto the term [C₁₃ +C₁₄ (C₁₅ -C₁₆)] in equation 7. The signal from summingmeans 150 is multiplied with signal E₇ by a multiplier 152 to providesignal E₈.

Referring now to FIG. 10, VI_(DWC).sbsb.O computer 70 includes amultiplier 155 multiplying signal E₆ with a direct current voltage C₁₈to provide a signal corresponding to the term C₁₈ (VI) in equation 8. Amultiplier 160 multiplies signal E₆ and API to provide a signal toanother multiplier 163 where it is multiplied with a direct currentvoltage C₂₁. Multiplier 163 provides a signal corresponding to the termC₂₁ (API)(VI) in equation 8. A multiplier 167 multiplies signals API andRI to provide a signal which is multiplied with a direct current voltageC₂₀ by a multiplier 170 which provides a signal corresponding to theterm C₂₀ (RI)(API). Signals S and API are multiplied by a multiplier 174to provide a signal to yet another multiplier 176 where it is multipliedwith a direct current voltage C₂₂. Multiplier 176 provides a signalcorresponding to the term C₂₂ (API)(S). A multiplier 180 effectivelysquares signals S and provides a signal to another multiplier 184 whereit is multiplied with direct current voltage C₁₉. Multiplier 184provides a signal corresponding to the term C₁₉ (S)².

Summing means 188 effectively sums the positive term in equation 8 bysumming the signals from multipliers 163 and 184 with a direct currentvoltage C₁₇ to provide a sum signal. Multiplier 190 effectively sums thenegative terms in equation 8 when it sums the signals from multipliers155, 170 and 176 to provide a sum signal. Subtracting means 195subtracts the sum signal provided by summing means 190 from the sumsignal provided by summing means 188 to provide signal E₁₀.

VI_(DWC).sbsb.P computer 72 shown in FIG. 11, includes a naturallogarithm function generator 200 receiving signal E₈ and providing asignal corresponding to the term ln SUS₂₁₀ to multipliers 201 and 202.Multiplier 201 multiplies the signal from function generator 200 with adirect current voltage C₂₄ to provide a signal corresponding to the termC₂₄ ln SUS₂₁₀ in equation 9. Multiplier 202 effectively squares thesignal from function generator 200 to provide a signal that ismultiplied with the direct current voltage C₂₅ by a multiplier 205.Multiplier 205 provides a signal corresponding to the term C₂₅ (lnSUS₂₁₀)² in equation 9. Subtracting means 206 subtracts the signalsprovided by multiplier 201 from the signal provided by multiplier 205.Summing means 207 sums the signal from subtracting means 206 with adirect current voltage C₂₃. A multiplier 208 multiplies the sum signalsfrom summing means 207 with a direct current voltage POUR to provide asignal which is summed with signal E₁₀ by summing means 210 whichprovides signal E.sub. 11.

Referring now to FIG. 12, ΔRI computer 79 includes multipliers 220, 225and 227 which effectively square signals E₆, E₁₂ and KV ₂₁₀,respectively. Multipliers 230 and 231 multiply signal KV₂₁₀ with signalsE₁₂ and API, respectively. Multipliers 235, 236 multiply signal S withsignals API and E₆, respectively, to provide product signals while amultiplier 238 multiplies signal E₁₂ with a direct current voltage C₂₇to provide a signal corresponding to the term C₂₇ (ΔVI). Multipliers221, 240, 241, 242, 243, 244 and 245 multiply the product signals frommultipliers 220, 225, 230, 227, 231, 235 and 236, respectively, withdirect current voltages C₂₉, C₃₄, C₃₁, C₂₈, C₃₀, C₃₂ and C₃₃,respectively, to provide signals corresponding to the term C₁₉ (VI)²,C₃₄ (ΔVI)², C₃₁ (ΔVI), C₂₈ (KV₂₁₀)², C₃₀ (KV₂₁₀)(API), C₃₂ (API)(S) andC₃₃ (VI)(S), respectively.

Summing means 250 effectively sums the positive terms of equation 11 andsum signals from multipliers 221, 241 and 244 with a direct currentvoltage C₂₆ to provide a sum signal. Summing means 253 effectively sumsthe negative terms of equation 11 when it sums the signals frommultipliers 238, 240, 242 and 243 to provide a sum signal. Subtractingmeans 255 subtracts the signal provided by summing means 253 from thesignal provided by summing means 250 to provide a signal to a multiplier257. Multiplier 257 multiplies the signal with a direct current voltageC₃₅ to provide signal ΔRI.

Referring now to FIG. 13, J computer 80 includes multipliers 272 and 273multiplying signals S and ΔRI, respectively, with direct currentvoltages C₄₃ and C₃₇, respectively, to provide signals corresponding tothe terms C₄₃ (S) and C₃₇ (ΔRI), respectively, in equation 12.Multipliers 270, 271 and 278 effectively square signals E₆, S and T toprovide signals to multipliers 280, 281 and 282, respectively, wherethey are multiplied with direct current voltages C₃₉, C₃₈ and C₄₀,respectively. Multipliers 280, 281 and 282 provide signals correspondingto the terms C₃₉ (VI)², C₃ (S)² and C₄₀ (T)², respectively. Multiplier284 multiplies signals T and KV₂₁₀ to provide a signal to a multiplier285 where it is multiplied with a direct current voltage C₄₂. Multiplier285 provides a signal corresponding to the term C₄₂ (KV₂₁₀)(T) inequation 12. Signals S and T are multiplied by a multiplier 288 toprovide a signal to yet another multiplier 290 where it is multipliedwith a direct current voltage C₄₁. Multiplier 290 provides a signalcorresponding to the term C₄₁ (S)(T). Signals T and ΔRI are multipliedby a multiplier 295 which provides a signal to a multiplier 297 where itis multiplied with a direct current voltage C₄₄ to provide a signalcorresponding to the term C₄₄ (ΔRI)(T). A multiplier 300 multipliessignals E₁₂ and ΔRI to provide a signal to a multiplier 303 where it ismultipled with a direct current voltage C₄₅ which provides a signalcorresponding to the term C₄₅ (ΔVI)(ΔRI) in equation 12.

Summing means 305 effectively sums all positive terms of equation 12when it sums a direct current voltage C₃₆ with the signals frommultipliers 273, 281, 282, 290 and 303 to provide a sum signal. A sumsignal corresponding to the summation of the negative terms in equation12 is provided by summing means 306 which sums the signals frommultipliers 272, 280, 285 and 297. Subtracting means 310 subtracts thesignal provided by summing means 306 from the signal provided by summingmeans 305 to create signal E₁₃.

The present invention as hereinbefore described controls an MP refiningunit receiving medium sour charge oil to achieve a desired charge oilflow rate for a constant MP flow rate. It is also within the scope ofthe present invention, as hereinbefore described, to control the MP flowrate while the medium sour charge oil flow is maintained at a constantrate.

What is claimed is:
 1. A control system for an N-methyl-2-pyrrolidonerefining unit receiving medium sour charge oil andN-methyl-2-pyrrolidone solvent, one of which is maintained at a fixedflow rate while the flow rate of the other is controlled by the controlsystem, treats the received medium sour charge oil with the receivedN-methyl-2-pyrrolidone to yield extract mix and raffinate, comprisinggravity analyzer means for sampling the medium sour charge oil andproviding a signal API corresponding to the API gravity of the mediumsour charge oil, viscosity analyzer means for sampling the medium sourcharge oil and providing signals KV₁₅₀ and KV₂₁₀ corresponding to thekinematic viscosities, corrected to 150° F. and 210° F., respectively,sulfur analyzer means for sampling the medium sour charge oil andproviding a signal S corresponding to the sulfur content of the mediumsour charge oil, a refractometer samples the medium sour charge oil andprovides a signal RI corresponding to the refractive index of the mediumsour charge oil, flow rate sensing means for sensing the flow rates ofthe medium sour charge oil and of the N-methyl-2-pyrrolidone andproviding signals CHG and SOLV, corresponding to the medium sour chargeoil flow rate and the N-methyl-2-pyrrolidone flow rate, respectively,temperature sensing means for sensing the temperature of the extract mixand providing a corresponding signal T, VI signal means connected to theviscosity analyzer means for providing a signal VI, corresponding to theviscosity index of the medium sour charge oil, in accordance withsignals KV₁₅₀ and KV₂₁₀, ΔVI signal means connected to the gravityanalyzer means, to the sulfur analyzer means, to the refractometer, tothe viscosity analyzer means and to the VI signal means for providing asignal ΔVI corresponding to a difference between the viscosities of themedium sour charge oil and the refined oil in accordance with signals S,API, KV₂₁₀, RI and VI, ΔRI signal means connected to the gravityanalyzer means, to the sulfur analyzer means, to the viscosity analyzermeans, and to the ΔVI signal means for providing a signal correspondingto the difference between the refractive indexes of the medium sourcharge oil and the refined oil, J signal means connected to the VIsignal means, to the temperature sensing means, to the viscosityanalyzer means, to the sulfur analyzer means, to the ΔRI signal meansand to the ΔVI signal means for providing a signal J, corresponding tothe N-methyl-2-pyrrolidone dosage, and control means connected to the Jsignal means and to the flow rate sensing means for providing a controlsignal in accordance with the J signal and one of the sensed flow ratesignals, and apparatus means connected to the control means forcontrolling the one flow rate of the medium sour charge oil andN-methyl-2-pyrrolidone flow rates in accordance with the control signal.2. A system as described in claim 1 in which the ΔVI signal meansincludes SUS₂₁₀ signal means connected to the viscosity analyzer meansfor providing a signal SUS₂₁₀ corresponding to the medium sour chargeoil viscosity in Saybolt Universal Seconds corrected to 210° F.; and ΔVInetwork means connected to the gravity analyzer means, sulfur analyzermeans, to the refractometer, to the VI signal means, to the J signalmeans and to the SUS₂₁₀ signal means and receiving voltage VI_(RP) forproviding signal ΔVI to the J signal means in accordance with signalsVI, S, API, RI, SUS₂₁₀ and voltage VI_(RP).
 3. A system as described inclaim 2 in which the SUS₂₁₀ signal means includes SUS signal meansconnected to the viscosity analyzer means, and receiving direct currentvoltages C₅ through C₁₂ for providing a signal SUS corresponding to aninterim factor SUS in accordance with signal KV₂₁₀, voltages C₅ throughC₁₂ and the following equation:

    SUS=C.sub.5 (KV.sub.210)+[C.sub.6 +C.sub.7 (KV.sub.210)]/[C.sub.8 +C.sub.9 (KV.sub.210)+C.sub.10 (KV.sub.210).sup.2 +C.sub.11 (KV.sub.210).sup.3 ](C.sub.12),

where C₅ through C₁₂ are constants; and SUS₂₁₀ network means connectedto the SUS signal means and to the ΔVI signal means and receiving directcurrent voltages C₁₃ through C₁₆ for providing signal SUS₂₁₂ to the ΔVIsignal means in accordance with signal SUS, voltages C₁₃ through C₁₆ andthe following equation:

    SUS.sub.210 =[C.sub.13 +C.sub.14 (C.sub.15 -C.sub.16)]SUS,

where C₁₃ through C₁₆ are constants.
 4. A system as described in claim 3in which the VI signal means includes K signal means receiving directcurrent voltages C₂, C₃, C₄ and T₁₅₀ for providing a signal K₁₅₀corresponding to the kinematic viscosity of the charge oil corrected to150° F. in accordance with voltages C₂, C₃, C₄ and T₁₅₀, and thefollowing equation:

    K.sub.150 =[C.sub.2 -ln (T.sub.150 +C.sub.3)]/C.sub.4,

where C₂ through C₄ are constants, and T₁₅₀ corresponds to a temperatureof 150° F.; H₁₅₀ signal means connected to the viscosity analyzer meansand receiving a direct current voltage C₁ for providing a signal H₁₅₀corresponding to a viscosity H value for 150° F. in accordance withsignal KV₁₅₀ and voltage C₁ in the following equation:

    H.sub.150 =lnln (KV.sub.150 +C.sub.1),

where C₁ is a constant; H₂₁₀ signal means connected to the viscosityanalyzer means and receiving voltage C₁ for providing signal H₂₁₀corresponding to a viscosity H value for 210° F. in accordance withsignal KV₂₁₀, voltage C₁ and the following equation:

    H.sub.210 =lnln (KV.sub.210 +C.sub.1),

H₁₀₀ signal means connected to the K signal means, to the H₁₅₀ signalmeans and the H₂₁₀ signal means for providing a signal H₁₀₀corresponding to a viscosity H value for 100° F., in accordance withsignals H₁₅₀, H₂₁₀ and K₁₅₀ and the following equation:

    H.sub.100 =H.sub.210 +(H.sub.150 -H.sub.210)/K.sub.150,

Kv₁₀₀ signal means connected to the H₁₀₀ signal means and receivingvoltage C₁ for providing a signal KV₁₀₀ corresponding to a kinematicviscosity for the charge oil corrected to 100° F. in accordance withsignal H₁₀₀, voltage C₁, and the following equation:

    KV.sub.100 =exp[exp(H.sub.100)]-C.sub.1,

and VI memory means connected to the KV₁₀₀ signal means and to theviscosity analyzer means having a plurality of signals stored therein,corresponding to different viscosity indexes and controlled by signalsKV₁₀₀ and KV₂₁₀ to select a stored signal and providing the selectedstored signal as signal VI.
 5. A system as described in claim 4 in whichthe ΔVI network means includes a VI_(DWC).sbsb.O signal means connectedto the gravity analyzer means, the sulfur analyzer means, therefractometer, and the VI signal means, and receives direct currentvoltages C₁₇ through C₂₂ and provides a signal VI_(DWC).sbsb.O inaccordance with signals RI, VI, S and API, voltages C₁₇ through C₂₂ andthe following equation:

    VI.sub.DWC.sbsb.O =C.sub.17 -C.sub.18 (VI)+C.sub.19 (S).sup.2 -C.sub.20 (RI)(API)+C.sub.21 (API)(VI)C.sub.22 (API)(S),

where C₁₇ through C₂₂ are constants; a VI_(DWC).sbsb.P signal meansconnected to the VI_(DWC).sbsb.O signal means and to the SUS₂₁₀ signalmeans for providing a VI_(DWC).sbsb.P signal in accordance with signalsSUS₂₁₀ and VI_(DWC).sbsb.O, voltages C₂₃ through C₂₅ and Pour, and thefollowing equation:

    VI.sub.DWC.sbsb.P =VI.sub.DWC.sbsb.O +(POUR)[C.sub.23 -C.sub.24 ln SUS.sub.210 +C.sub.25 (ln SUS.sub.210).sup.2 ],

where C₂₃ through C₂₅ are constants, and subtracting means connected tothe J signal means and to the VI_(DWC).sbsb.P signal means and receivingvoltage VI_(RP) for subtracting signal VI_(DWC).sbsb.P from voltageVI_(RP) to provide the ΔVI signal to the J signal means.
 6. A system asdescribed in claim 5 in which the ΔRI signal means receives directcurrent voltages corresponding to constants C₂₆ through C₃₅ and providessignal ΔRI in accordance with the received voltages, signals ΔVI, KV₂₁₀,VI, API and S and the following equation:

    ΔRI=[C.sub.26 -C.sub.27 (ΔVI)-C.sub.28 (KV.sub.210).sup.2 +C.sub.29 (VI).sup.2 -C.sub.30 (KV.sub.210)(API)+C.sub.31 (ΔVI)(KV.sub.210)+C.sub.32 (API)(S)-C.sub.33 (VI)(S)-C.sub.34 (ΔVI).sup.2 ]C.sub.35.


7. A system as described in claim 6 in which the J signal means receivesdirect current voltages corresponding to constants C₃₆ through C₄₅ andprovides the J signal in accordance with the received direct currentvoltages, signals ΔRI, S, VI, T, KV₂₁₀ and ΔVI, and the followingequation:

    J=C.sub.36 +C.sub.37 (ΔRI)+C.sub.38 (S).sup.2 -C.sub.39 (VI).sup.2 -C.sub.40 (T).sup.2 +C.sub.41 (S)(T)-C.sub.42 (KV.sub.210)(T)-C.sub.43 (S)-C.sub.44 (ΔRI)(T)+C.sub.45 (ΔRI)(ΔVI).


8. A system as described in claim 7 in which flow rate of the mediumsour charge oil is controlled and the flow of the N-methyl-2-pyrrolidoneis maintained at a constant rate and the control means receives signalSOLV from the flow rate sensing means, the J signal from the J signalmeans and a direct current voltage corresponding to a value of 100 andprovides a signal C to the apparatus means corresponding to a new mediumsour charge oil flow rate in accordance with the selected J signal,signal SOLV and the following equation:

    C=(SOLV)(100)/J,

so as to cause the apparatus means to change the medium sour charge oilflow to the new flow rate.
 9. A system as described in claim 7 in whichthe controlled flow rate is the N-methyl-2-pyrrolidone flow rate and theflow of the medium sour charge oil is maintained constant, and thecontrol means is connected to the sensing means, to the J signal meansand receives a direct current voltage corresponding to the value of 100for providing a signal SO corresponding to a new N-methyl 2-pyrrolidoneflow rate in accordance with signals CHG and the J signal and thereceived voltage, and the following equation:

    SO=(CHG)(J)/100,

so as to cause the N-methyl-2-pyrrolidone flow to change to the new flowrate.